<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <canvas width="600" height="400"></canvas>
    <script>
        let canvas = document.querySelector('canvas');
        let ctx = canvas.getContext('2d');

        // 第一个点
        ctx.moveTo(300,200);
        // 第二个点和第三个点的坐标以及圆弧的半径
        ctx.arcTo(300,250,250,250,25);
        ctx.stroke();
    </script>
</body>
</html>